1. Technical Field
Exemplary aspects of the present invention relate to an image forming apparatus such as a copier, a printer, a facsimile machine, a plotter, or a multi-function peripheral having at least two of copying, printing, facsimile, and plotter functions. More particularly, exemplary aspects of the present invention relate to an image forming apparatus capable of using a special color toner in addition to process color toners.
2. Description of the Related Art
Certain contemporary electrophotographic apparatuses are capable of using special toners in addition to process color toners of cyan, magenta, yellow, and black (CMYK). Such an electrophotographic apparatus includes one or more image forming stations (process units) for the special color toners in addition to four image forming stations for the respective process color toners of CMYK. Moreover, in the image forming station of the process color toner, the process color toner can be replaced with the special color toner. One of the special color toners is a clear toner (including a transparent toner, a colorless toner, an achromatic color toner, and a no-pigment toner).
For example, the electrophotographic apparatus can print color printed matter by entirely or partially overlaying the clear toner to adjust glossiness of the color printed matter. Such glossiness adjustment can generate higher value-added printed matter. Other special color toners include red (R), green, (G), and blue (B) toners. The use of such special color toners of RGB can reproduce high-quality colors that are difficult to reproduce by overlaying the CMYK process color toners. In addition to these special color toners, there is a wide variety of special color toners.
When a special color toner is used, a toner in the image forming station of the electrophotographic apparatus may need to be replaced. The toner replacement is needed in the following cases: a) where a process color toner is replaced with a special color toner; b) where a special color toner is replaced with a process color toner; c) where a special color toner is replaced with another special color toner; and d) a process color toner is replaced with another process color toner.
JP-4321583-B1 (JP-2008-151971-A) discloses an image forming method performed by an image forming apparatus including four cartridge holders, in which CMYK toner cartridges in the image forming apparatus are replaced with special color toner cartridges. Prior to the replacement, a suitable order in which toners are overlaid to form a desired image is determined. Accordingly, a user sets a suitable toner cartridge in the determined cartridge holder. When the toner cartridge is replaced, the cartridge holder reads toner attribute information provided in the toner cartridge that the image forming apparatus can use to monitor which color of toner cartridge is set in which cartridge holder. According to the image forming method disclosed in JP-4321583-B1 (JP-2008-151971-A), the image forming apparatus with such a configuration including the four process units can reproduce diverse colors difficult to reproduce by overlaying CMYK process color toners, while remaining compact.
In the method disclosed in JP-4321583-B1 (JP-2008-151971-A), since the toner cartridge (process cartridge) as a whole is replaced, different types of toners are not mixed together. That is, when the process cartridge is replaced, a development device in which developer is stored is detached from the image forming apparatus. The detachment of the development device prevents admixture of a developer of the replaced process cartridge and a developer of a replacement process cartridge.
Meanwhile, devices for replenishing toner to a development device or a development unit using a toner replenishing member are known. The toner replenishing member, called a toner bottle or a toner tank, is disposed in a position different from the development device arranged inside a process cartridge detachable to an image forming apparatus or the development unit replaceable to the image forming apparatus. The arrangement of the toner replenishing member enables the process cartridge to be compact. Moreover, replacement of the toner replenishing member can maintain appropriate life span of the process cartridge.
In the image forming apparatus employing the toner replenishing method using the toner replenishing member, however, a mixture of toners cannot be avoided where toner replacement involving a special toner is performed as described above. That is, even if the toner replenishing member and the development unit are replaced as appropriate depending on the purpose for which the toner is used, a last-used toner of a type different from that of the special toner remains in a toner replenishing path serving as a toner supply unit. Thus, if the image forming apparatus forms an image as is, the different types of toners may cause a color mixture (contamination, mixing) that is not intended by a user. Consequently, the color mixture may cause generation of an irregular image.
The color mixture may be prevented if the toner supply unit is replaced at the same time as the replacement of the toner replenishing member and the development unit. However, since the toner supply unit includes a conveyance tube, a pump, and a hopper, the replacement of the toner supply unit on each such occasion is not only a cumbersome process, but also may damage an image forming unit. Accordingly, the toner supply unit arranged between the toner replenishing member and the development unit should not be replaced from a practical standpoint.
Alternatively, an image forming apparatus may be configured to include a dedicated special toner image forming unit for each of CMYK image forming units, so that toner replacement is not needed to avoid a problem of the color mixture. However, such a configuration increases the overall size of the image forming apparatus, and limits the types of color changes that can be made by toner replacement.
Conventionally, a so-called five-station image forming apparatus is known, in which one image forming unit just for a special toner is disposed in addition to CMYK image forming units. However, in a case where two or more image forming units are to be added, a concomitant increase in size of the image forming apparatus may become a serious problem.